Manufacture of improved metakaolin by grinding and use in cement-based composites and alkali-activated systems

ABSTRACT

In one embodiment, the present invention relates to a method of making a highly reactive pozzolan, involving the steps of forming a slurry comprising metakaolin and a liquid; wet milling the slurry; and separating the metakaolin from the liquid to provide the highly reactive pozolan. In another embodiment, the present invention relates to a method of making a cement-based composition involving the steps of providing a highly reactive pozzolan by forming a slurry comprising metakaolin and a liquid, wet milling the slurry, and separating the metakaolin from the liquid; and combining the highly reactive pozzolan with at least one cementitious material.

FIELD OF THE INVENTION

[0001] This invention relates to novel methods of making a metakaolinmaterial well suited for cement-based composites and alkali-activatedsystems.

BACKGROUND OF THE INVENTION

[0002] The use of metakaolin in cement is known. For example, U.S. Pat.No. 4,793,861 describes a cement-based product which is reinforced withglass fibers having good resistance to alkaline environments. Theproduct contains, for each 100 parts by weight of cement, about 10 to 40parts by weight of metakaolin, the latter exhibiting a reactivity to themodified Chapelle test greater than 500 mg of CaO per gram ofmetakaolin.

[0003] U.S. Pat. No. 4,842,649 describes a blended hydraulic cementcomposition composed of portland cement, slag, pozzolans includingmetakaolin, and admixtures including potassium carbonate and waterreducing compositions.

[0004] U.S. Pat. No. 4,975,396 describes a process for producingreinforced cementitious compositions in which the following constituentsare mixed in the aqueous phase in the following order: about 35-55 partsby weight of water mixed with about 3-12 parts of a polymer, by weightof dry polymer; up to about 5 parts of a water-reducing auxiliary agentand/or a liquefying agent; from about 15-30 parts of metakaolin; fromabout 50-120 parts of silica sand; and about 100 parts of cement.Continuous mixing is maintained until a homogeneous, thixotropic pasteis obtained. Then between 2 and 15% by weight of alkaline-resistantglass fibers, relative to the weight of the paste, is introduced intothe paste.

[0005] U.S. Pat. No. 4,994,114 describes method for selecting a pozzolan(for example metakaolin) for incorporation into a composite materialcomprising cement and glass.

[0006] U.S. Pat. No. 5,167,710 describes a process for making a cementmixture containing fibers wherein a paste is formed by mixing cementand, per 100 parts by weight of cement, approximately 5 to 20 parts byweight of a first pulverized material of which the grains have anaverage diameter of between ⅕ and {fraction (1/10)} of the averagediameter of the grains of the cement and approximately 20 to 35 parts byweight of water. The paste is then mixed with reinforcing fibers. Thepaste may also include a second pulverized material the average graindiameter of which is between ⅕ and {fraction (1/10)} of the averagediameter of the first pulverized material.

[0007] U.S. Pat. No. 5,372,640 describes cement-based productsreinforced with alkali-resistant glass fibers that become almostinsensitive to aging when 30 to 40 parts by weight of a metakaolincomposition are added for each 100 parts of cement.

[0008] U.S. Pat. No. 5,624,489 describes a conversion-preventingadditive for high-alumina cement-based compositions, the additivecomprising: siliceous pozzolanic powder, e.g. zeolite, granulatedblast-furnace slag, fly ash, silica fume, rice hulls, metakaolin;inorganic salts containing sodium or potassium cations and sulphate,carbonate, nitrate, silicate, phosphate, chloride or bromide anions, andoptionally other chemical admixtures, e.g. superplasticizers.

[0009] U.S. Pat. No. 5,626,665 describes cementitious systems comprisedof gypsum, calcined clay, and clinker.

[0010] Pozzolans are finely divided materials which can react withalkali to form cementitious products. The fine particle size and largepore volume of pozzolans, however, can lead to an increase in waterdemand. In cement-based systems, the addition of extra water can reducethe performance of the system by reducing the strength and increasingthe permeability of the resultant cement-based structures. Thediminished strength is undesirable for several reasons. Initially, delayin early strength development results in surface cracking due toevaporation. Secondly, jobs take longer because the concrete form mustremain in place substantially longer, and finishing is delayed.

[0011] Reactive pozzolans can be made by dry grinding metakaolin usingball milling. However, ball milling is an expensive and time consumingprocess. In this connection, ball milling often requires 6 hours ofmilling time. Such long processing times restricts the commercialmanufacturability of dry milled pozzolans. Dry milling is not thereforefrequently employed on the raw metakaolin. However, the addition ofmetakaolin to finishing mills or mills for clinker or slag grinding (drymilling) is employed for incorporating pozzolans into cement-basedsystems.

[0012] Nevertheless, there is still a need for pozzolans having improvedactivity to provide cement-based systems and alkali activated systemshaving lower water demand and higher compressive strength, as well asimproved flowability as a dry powder and a higher bulk density to reduceshipping and storage costs.

SUMMARY OF THE INVENTION

[0013] This invention relates to cement-based compositions containing ahighly reactive pozzolan based upon a wet milled metakaolin. Thecement-based compositions have lower water demand and equivalent orimproved flowability in dry form compared to conventional cement-basedcompositions. Resultant structures or composites made from thecement-based compositions according to the present invention have highcompressive strength compared to structures made from cement-basedcompositions made with conventional pozzolans (dry milled metakaolin andunprocessed metakaolin).

[0014] In one embodiment, the present invention relates to a method ofmaking a highly reactive pozzolan, involving the steps of forming aslurry comprising metakaolin and a liquid; wet milling the slurry; andseparating the metakaolin from the liquid to provide the highly reactivepozzolan.

[0015] In another embodiment, the present invention relates to a methodof making a cement-based composition involving the steps of providing ahighly reactive pozzolan by forming a slurry comprising metakaolin and aliquid, wet milling the slurry, and separating the metakaolin from theliquid; and combining the highly reactive pozzolan with at least onecementitious material.

[0016] In yet another embodiment, the present invention relates to amethod of making an alkali-activated composition involving the steps ofproviding a highly reactive pozzolan by forming a slurry comprisingmetakaolin and a liquid, wet milling the slurry for a period of timefrom about 2 minutes to about 30 minutes, and separating the metakaolinfrom the liquid; and combining the highly reactive pozzolan with atleast one geopolymeric material.

[0017] In still yet another embodiment, the present invention relates toa method of making a highly reactive pozzolan composition involving thesteps of forming a slurry comprising from about 20% to about 80% byweight of metakaolin and from about 20% to about 80% by weight of aliquid and wet milling the slurry for a period of time from about 1minute to about 60 minutes to provide the highly reactive pozzolancomposition.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The cement-based compositions of this invention are intended foruse in cement-based applications such as swimming pool plasters, grouts,mortars and concrete. The alkali-activated compositions of thisinvention are intended for use in geopolymer and zeolitic applicationssuch as the formation of cast and molded bodies, the storage of toxicchemicals and radioactive waste, and in specialty concretes. Thecement-based composites or compositions of the present invention containat least one cementitious material, at least one highly reactivepozzolan, and optionally at least one dispersant. The cement-basedcomposition is the total combined dry mixture of the cementitiouscomposition and highly reactive pozzolan materials which react withwater to form the binder in concrete or other material. Concrete is aconstruction material comprised of the cement-based composition, water,optional admixtures, and aggregates.

[0019] Cementitious materials include those materials typically requiredto make cement; that is, those materials that can react with lime orother alkali and exhibit cementing properties. Generally speaking,cementitious materials are binder materials that harden to form aconnecting medium between solids. Cementitious materials includecements, which are any mixture of finely-ground lime, alumina, andsilica that will set to a hard product that combines with otheringredients to form a hydrate such as portland cement, hydrauliccements, blended cement, and masonry cement, mortar, and relatedaggregate, admixtures and/or additives including hydrated lime,limestone, chalk, calcareous shell, talc, slag or clay.

[0020] Ordinary portland cement is a hydraulic cement produced bypulverizing portland cement clinker. Portland cements are classifiedunder ASTM standards ©150-95 into eight types, including: Type I for usein general concrete construction where the special properties specifiedfor Types II, Ill, IV and V are not required; Type II for use in generalconcrete construction exposed to moderate sulphate action, or wheremoderate heat of hydration is required; Type III for use when high earlystrength is required; Type IV for use when low heat of hydration isrequired; Type V for use when high sulphate resistance is required; andTypes IA, IIA and IIIA, which are the same as Types I, II and III,respectively, except that they have an air entraining agent added.“Ordinary portland cement” in the context of this invention includes alltypes (I-V and IA-IIIA) of portland cement as referenced in ASTM C150-95, including any cement blends thereof.

[0021] In one embodiment, the cement-based compositions of the presentinvention contain from about 50% to about 99.5% by weight of acementitious material. In another embodiment, the cement-basedcompositions of the present invention contain from about 75% to about99% by weight of a cementitious material.

[0022] The alkali-activated systems of the present invention contain atleast one geopolymeric material, at least one highly reactive pozzolan,and optionally at least one dispersant. Many geopolymeric materials aredescribed in U.S. Pat. Nos. 4,509,985; 5,342,595; and 5,352,427, whichare incorporated by reference for their teachings in this regard.Geopolymeric materials include one or more of alumino-silicate oxide,strong alkalis such as sodium hydroxide and potassium hydroxide, water,sodium and potassium silicates, M₂O compounds such as one or more ofNa₂O, K₂O, zeolites, silica, alumina and other metal oxides. Generaly,alkali-activated compositions are formed by reacting specific ratios ofsilica and alumina with various alkali compounds. In the presentinvention, the amount of alkali that is placed in an aqueous slurrycontaining metakaolin while remaining fluid is primarily dependent uponthe absorption/adsorption characteristics of the metakaolin.

[0023] In one embodiment, the alkali-activated systems of the presentinvention contain from about 40% to about 99.5% by weight of one or moregeopolymeric materials. In another embodiment, the alkali-activatedsystems of the present invention contain from about 70% to about 99% byweight of one or more geopolymeric materials.

[0024] The cement-based compositions and the alkali-activated systemscontain at least one highly reactive pozzolan. The cement-basedcompositions and the alkali-activated systems according to the presentinvention have at least one of lower water demand, higher compressivestrength, and higher flowability in the fluid state compared withcement-based compositions and alkali-activated systems that do notcontain a highly reactive pozzolan according to the present invention.

[0025] In one embodiment, the cement-based compositions of the presentinvention contain from about 0.5% to about 50% by weight of a highlyreactive pozzolan. In another embodiment, the cement-based compositionsof the present invention contain from about 1% to about 25% by weight ofa highly reactive pozzolan. In yet another embodiment, the cement-basedcompositions of the present invention contain from about 2% to about 20%by weight of a highly reactive pozzolan.

[0026] In one embodiment, the alkali-activated systems of the presentinvention contain from about 0.5% to about 50% by weight of a highlyreactive pozzolan. In another embodiment, the alkali-activated systemsof the present invention contain from about 1% to about 25% by weight ofa highly reactive pozzolan. In yet another embodiment, thealkali-activated systems of the present invention contain from about 2%to about 20% by weight of a highly reactive pozzolan.

[0027] The highly reactive pozzolan is highly reactive in that thehighly reactive pozzolan has an increased dissolution of silicon andaluminum and a decreased absorption of water and potassium silicate incomparison to conventional metakaolin.

[0028] The highly reactive pozzolan is highly reactive further in thatcomposites having at least one of high compressive strengths and lowwater demand are obtainable as a result of the present invention. Thatis, the components of the cement-based compositions and thealkali-activated systems of the present invention containing the highlyreactive pozzolan react and set in such a manner that composites havinghigh compressive strengths are obtained compared with cement-basedcompositions and the alkali-activated systems that do not contain thehighly reactive pozzolan as described herein. Although the highlyreactive pozzolan possesses little or no cementitious value, in thepresence of moisture it chemically reacts with a hydroxide, such ascalcium hydroxide, at ordinary temperatures to form compounds possessingcementitious properties.

[0029] The highly reactive pozzolan is in the form of particles and/oragglomerated beads of microparticles of metakaolin treated in the mannerdescribed below. The highly reactive pozzolan may be pulverized ornon-pulverized. In one embodiment, the particles and/or agglomeratedbeads have a median particle size from about 10 microns to about 100microns (above about 10 microns). In another embodiment, the particlesand/or agglomerated beads have a median particle size from about 15microns to about 75 microns (above about 15 microns). In yet anotherembodiment, the particles and/or agglomerated beads have an averageparticle size from about 20 microns to about 50 microns (above about 20microns).

[0030] In a preferred embodiment, the particle size distribution of theparticles and/or agglomerated beads is about 95% by weight of themicroparticles are from about 10 microns to about 75 microns. In anotherpreferred embodiment, the particle size distribution of the particlesand/or agglomerated beads is about 95% by weight of the agglomeratedbeads are from about 15 microns to about 50 microns.

[0031] There are a number of methods and devices for measuring particlesizes in this range. For the purposes of this invention particle size isdetermined by conventional sedimentation techniques using Micromeretics,Inc.'s SEDIGRAPH(® 5100 particle size analyzer. Particles are slurriedin water with a dispersant and pumped through the detector withagitation to disperse loose agglomerates.

[0032] In one embodiment, the highly reactive pozzolans suitable for usein the present invention may be prepared by a process which comprisesforming a liquid slurry comprising at least one metakaolin, and wetgrinding the metakaolin liquid slurry. Such a slurry may be stored, andsubsequently used to form a cement-based composition or analkali-activated composition just prior to its intended use. In anotherembodiment, the highly reactive pozzolans suitable for use in thepresent invention may be prepared by a process which comprises forming aliquid slurry comprising at least one metakaolin, wet grinding themetakaolin liquid slurry, drying the wet milled metakaolin liquidslurry, and optionally pulverizing the dried wet milled metakaolin. In apreferred embodiment, the metakaolin combined with a liquid to form aslurry has a particle size from about 0.1 micron to about 5 microns. Thedesired particle size distributions of the metakaolin can be obtained bygrinding or pulverizing larger particles of metakaolin and/or throughscreening, centrifuging, air classification, or other separating meansfor removing undesirably sized particles, such as those larger thanabout 10 microns.

[0033] Metakaolin is known to those of ordinary skill in the art and canbe prepared by calcining hydrous kaolin, which is generally representedby the formula Al₂O₃2SiO₂2H₂O, where the water is present asinterstitial water. The metakaolin of this invention is typically madeby calcination at temperatures from about 350° C. to about 1000° C.,more typically from about 500° C. to about 900° C. The terms“metakaolin” and “metakaolinite” are used herein to mean an activatedproduct of kaolinite, produced thermally or by any other means. Theabbreviated formula for metakaolin can be written by using the standardsymbols A and S (A═Al₂O₃and S═SiO₂) as AS₂. In a preferred embodiment,the hydrous kaolin is not milled before it is heat treated to formmetakaolin.

[0034] A suitable amount of metakaolin is combined with a liquid to forma slurry. The liquid is typically water but may also include organicliquids and especially water-organic liquid mixtures. Optionally, aneffective amount of at least one dispersant is included in the slurry tofacilitate the dispersion of the metakaolin in the liquid. Thesedispersants may be preformed and added to the slurry or formed withinthe slurry. In one embodiment, the cement-based compositions and/or thealkali-activated systems also contain at least one dispersant.

[0035] The slurry is typically neutral, e.g., having a pH from about 6to about 8, and preferably from about 6.5 to about 7.5. The pH of theslurry may be adjusted, if necessary, by the addition of an acid or baseso that the final pH of the slurry is approximately neutral. Formationof the slurry is typically conducted at ambient temperature and atatmospheric pressure. Higher or lower temperatures and pressures may beused but are not necessary.

[0036] In one embodiment, the slurry contains from about 10% to about90% by weight of metakaolin and from about 10% to about 90% by weight ofliquid. In another embodiment, the slurry contains from about 20% toabout 80% by weight of metakaolin and from about 20% to about 80% byweight of liquid. In yet another embodiment, the slurry contains fromabout 30% to about 70% by weight of metakaolin and from about 30% toabout 70% by weight of liquid.

[0037] Dispersants suitable for use in the present invention includeorganic dispersants and inorganic dispersants. Dispersants generallyinclude ammonia-based dispersants and phosphate-based dispersants.Dispersants further include sulfonate dispersants, carboxylic aciddispersants and polymeric dispersants, such as polyacrylate dispersants.

[0038] In one embodiment, from about 0.1% to about 20% by weight of themetakaolin of one or more dispersants is added to the slurry. In anotherembodiment, from about 0.5% to about 10% by weight of the metakaolin ofone or more dispersants is added to the slurry. In yet anotherembodiment, from about 1% to about 8% by weight of the metakaolin of oneor more dispersants is added to the slurry.

[0039] Inorganic phosphate-based dispersants include diammoniumphosphate, dipotassium phosphate, disodium phosphate, monoammoniumphosphate, monopotassium phosphate, monosodium phosphate, potassiumtripolyphosphate, sodium acid pyrophosphate, sodium hexametaphosphate,sodium tripolyphosphate, tetrapotassium pyrophosphate, tetrasodiumpyrophosphate, tripotassium phosphate, trisodium phosphate, ureaphosphate and mixtures thereof.

[0040] Sulfonate dispersants include naphthalene sulfonates,alkylnaphthalene sulfonates, ethoxylated alkylphenol sulfonates,petroleum sulfonates, fatty acid sulfonates, lignosulfonates, olefinsulfonates, amine sulfonates, and alkylaryl sulfonates. Specificexamples include those under the trade designation Morwet® availablefrom Witco Corp., those under the trade designation Sellogen availablefrom Henkel Corp., and those under the trade designation Emkaponavailable from Emkay Chemical Co.

[0041] Carboxylic acids typically include organic acids and theircorresponding salts containing from about 6 to about 25 carbon atoms. Inanother embodiment, carboxylic acids include organic acids and theircorresponding salts that contain from about 8 to about 20 carbon atoms.

[0042] Polyacrylates include polyacrylic acid, salts of acryliccopolymers, acrylic acid copolymers (for example with maleic acid), andammonium or alkali metal polyacrylates and polycarboxylate salts.Specific examples include those under the trade designations Acumer® andAcusol available from Rohm & Haas Co., those under the trade designationColloid available from Rhone-Poulenc Corp., and those under the tradedesignation Mayosperse available from Mayo Chemical.

[0043] In one embodiment, the cement-based compositions, thealkali-activated systems and/or the highly reactive pozzolan alsocontain at least one of water reducers and superplasticizers. A minoramount of a flocculating agent may also be incorporated into the mixtureto facilitate dispersion/suspension of the particles in the liquidmedium. In addition, materials other than metakaolin may be incorporatedinto the mixture. For example, a minor amount of special water-solubleor water-dispersible sorbents (e.g., silicas, aluminas or other clays)to selectively adsorb sulfur, soaps, phosphorous or other deleteriouscompounds may be incorporated into the mixture and end up in theagglomerated beads. Additional additive materials include gypsum, alkalisalts, hydrated kiln dust, hydrated lime, fly ash, plasticizing agents,etc.

[0044] In one embodiment, the cement-based compositions, thealkali-activated systems and/or the highly reactive pozzolans contain abinder such as carboxymethyl cellulose, polyvinyl alcohol and/orpolyvinylpyrrolidone. In another embodiment, the cement-basedcompositions, the alkali-activated systems and/or the highly reactivepozzolans do not contain a binder such as carboxymethyl cellulose,polyvinyl alcohol and/or polyvinylpyrrolidone. In a preferredembodiment, the highly reactive pozzolan composition does not contain abinder such as carboxymethyl cellulose, polyvinyl alcohol and/orpolyvinylpyrrolidone.

[0045] In another embodiment, the cement-based compositions, thealkali-activated systems and/or the highly reactive pozzolans contain aminor amount of at least one binder material, preferably a waterdispersible binder. As used herein, a “water dispersible binder” shallmean that under typical process conditions, the binder is soluble inwater or other liquid medium or is sufficiently dispersed or suspendedtherein. Binders suitable for use within the context of the presentinvention include alginates, dextrin, glucose, gums, starch, waxes,glues; polymeric compounds such as poly(vinylacetate); mineral acidssuch as sulfuric acid and phosphoric acid; phosphates such as ammoniumphosphate; silica compounds such as alkaline silicates and silicahydrosol; and colloidal clays such as attapulgite. These bindermaterials are typically present in an amount up to about 10% by weightof the highly reactive pozzolan on a moisture-free basis, preferablyfrom about 1% to about 5% by weight. Typically, the polymer compound, ifpresent as the only binder, is present in an amount up to about 3% byweight of the highly reactive pozzolan on a moisture-free basis; and thecolloidal clay, if present as the only binder, is present in an amountup to about 5% by weight of the highly reactive pozzolan on amoisture-free basis (as used herein in this context means the weightachieved after heating to a constant weight at about 250° F.).

[0046] The metakaolin slurry is then wet milled. Wet milling proceduresare known. Typically wet milling employs a drum mill, vertical mediamills, a sedimentary delaminator, or colloid/dispersion mill. Wetmilling may involve one or more of high intensty milling, moderateintensity mill and low intensity milling. Specific examples of wet millsinclude a Chaser mill, Cowles mill, a Colloid mill, a Duncan mill, aKady mill, a Morehouse mill, a Muller mill, a Netzsch mill, a Premiermill, a Kofthoff mill and various sedimentary delaminators.

[0047] In one embodiment, the metakaolin slurry is wet milled for aperiod of time from about 1 minute to about 60 minutes (less than about1 hour). In another embodiment, the metakaolin slurry is wet milled fora period of time from about 2 minutes to about 30 minutes (less thanabout 30 minutes). In yet another embodiment, the metakaolin slurry iswet milled for a period of time from about 2.5 minutes to about 15minutes (less than about 15 minutes). In still yet another embodiment,the metakaolin slurry is wet milled for a period of time from about 3minutes to about 10 minutes (less than about 10 minutes).

[0048] In one embodiment, the metakaolin slurry is wet milled at atemperature from about −10° C. to about 150° C. In this embodiment, anaqueous slurry contains an additive that either lowers the freezingpoint or raises the boiling point of water. In another embodiment, themetakaolin slurry is wet milled at a temperature from about 10° C. toabout 80° C. In yet another embodiment, the metakaolin slurry is wetmilled at a temperature from about 15° C. to about 70° C.

[0049] Wet milling decreases the pore volume of the particles and/oragglomerated beads of metakaolin. Comparing the metakaolin used to formthe slurry, and the highly reactive pozzolan made in accordance with thepresent invention (metakaolin after required processing), in oneembodiment, there is from about 5% to about 75% reduction in porevolume. In another embodiment, there is from about 10% to about 60%reduction in pore volume. In yet another embodiment, there is from about20% to about 50% reduction in pore volume.

[0050] The wet milled metakaolin slurry is dried in any suitable manner.For example, drying may be conducted by spray drying the slurry, flashdrying the slurry, rotary drying, apron drying the slurry, oven dryingthe slurry, mixing the slurry or other drying techniques. The timerequired for drying varies, and primarily depends upon the amount andidentity of the liquid in the slurry. Flash drying techniques are knownin the clay industry. Spray drying techniques are known in the clayindustry. As a reference, consult, e.g., “Atomization and Spray Drying,”by W. R. Marshall (Chemical Engineering Monograph Series, No. 2, Vol. 50(1954)), which is hereby incorporated by reference for its teachings inthis regard.

[0051] In spray drying, the mixture of metakaolin, liquid (preferablywater) and optional additives or ingredients is adjusted, if necessary,by the addition of liquid so that the metakaolin slurry is pumpable andsprayable. In one embodiment, the concentration of metakaolin in theslurry is at least 40% by weight of the slurry. In another embodiment,the concentration of metakaolin in the slurry is at least 50% by weightof the slurry. In yet another embodiment, the concentration ofmetakaolin in the slurry is at least 60% by weight of the slurry. It isnoted that due to rheological considerations, smaller interactiveparticles tend to make a viscous mix, so transport properties depend onthe size of the particles as well as their concentration. The mixture orslurry is then sprayed into an atmosphere of hot, inert gases (to thisproduct).

[0052] Spray dryers of various designs can be used. These dryers may beof the concurrent, countercurrent, or mixed flow type. Nozzles, disks orthe like can be used to disperse the slurry into droplets. Thetemperature of the inlet and outlet air of the spray dryer will depend,of course, on the design of the dryer. The actual internal temperatureof the agglomerated beads in the drying chamber should be below 225° F.,for example from about 180° F. to 200° F. At these temperatures, thereis very little or no change in the crystal structure of the clay (freewater is eliminated but interstitial water is not eliminated). Thedroplets thus become porous agglomerated beads of metakaolin and arecollected downstream of the drying chamber, by the usual methods. Usinga concurrent dryer, the air inlet temperature and the clay slurry feedrate are adjusted to produce an air outlet temperature within the rangefrom about 250° F. to about 300° F.

[0053] In another embodiment, the wet milled metakaolin (mixture ofmetakaolin, liquid and optional ingredients) can be agglomerated in amechanical mixer prior to drying. Mixing typically involves using ahigh-shear mixer. A preferred type of mixer employs pins or bladesmounted radially on a rotating shaft, so that the tip of the pin orblade, traveling at high speed, causes solid particles, binder and waterto impinge upon or contact each other in such a way as to form anagglomerate. In time, nominally-spherical particles tend to grow largerand larger. This phenomenon is enhanced by the tips of the blades orpins coming very close to a stationary wall or to a solid object (e.g.,another blade or pin) moving at a different relative rate. The vortexesset up by this shearing motion tend to enhance the sphericity of thegrowing beads.

[0054] Other less energy-intensive mechanical contacting processes areknown to those skilled in the art, including the use of drum or dishgranulators, fluidized or spouted bed granulators, or tumbling, rotary,vibratory or gyratory granulators. For descriptions of these processes,see, for example, Sherrington, P. J., Granulation, Heyden & Son, Ltd.,(1981), which is incorporated herein by reference for its teaching inthis regard. These and similar devices can be used to produce granules,although not all are optimum for making the instant invention.

[0055] Optionally after drying the wet milled metakaolin, the metakaolinproduct is pulverized in any suitable manner. Pulverization methods andapparatuses are known to those skilled in the art. For example,pulverization may be conducted using a high energy impact mill.

[0056] The highly reactive pozzolan contains from about 70% to about100% by weight of processed metakaolin (wet milled, dried, andoptionally pulverized) and from about 0% to about 30% of one or moredispersants and additives. In another embodiment, the highly reactivepozzolan contains from about 80% to about 99.5% by weight of metakaolinmicroparticles and from about 0.5% to about 20% of one or moredispersants and additives. In yet another embodiment, the highlyreactive pozzolan contains from about 90% to about 99% by weight ofmetakaolin microparticles and from about 1% to about 10% of one or moredispersants and additives.

[0057] In one embodiment, the highly reactive pozzolan is combined withone or more cementitious materials to form a cement-based composition.Cement paste is made by adding water to the cement-based composition.Swimming pool plaster, grouts, concrete and mortar are made by combiningwater, the cement-based composition, and any desired aggregate,admixtures or additives. In another embodiment, the highly reactivepozzolan is combined with one or more geopolymeric materials includingalkali containing products to form an alkali-activated system orcomposition for cast and molded bodies, the storage of toxic chemicalsand radioactive waste, and in specialty concretes.

[0058] ASTM C 109/109M-95 quantifies the compressive strength ofhydraulic cement mortars. The number following the ASTM test methodnumber indicates that it is the ASTM test method in effect during thatspecific year, such as 1995 in the case where 95 follows the ASTM testmethod. The compressive strength is the measured maximum resistance of aspecimen to axial compressive loading normally expressed as force perunit cross-sectional area. Although the ASTM test methods are set outspecifically, those skilled in the art may be aware of alternativemethods which could be used to test for the referenced qualities orresults. The only difference being, the results or qualities may bereported in a different manner wherein a conversion system could be usedto give comparable results. Consequently, the invention should not belimited by the referenced test methods and the results thereof, butrather only to the claims as set forth below taking into accountequivalent testing methods and results.

[0059] Examples of this invention are included hereinbelow. Of course,the examples are not intended as limiting this invention as modificationof the examples by ordinary expedient will be readily apparent to thoseof ordinary skill in the art. Unless otherwise indicated in thefollowing examples and elsewhere in the specification and claims, allparts and percentages are by weight, temperatures are in degreesCelsius, pressures are at or near atmospheric.

[0060] Several mortar compositions, both according to the presentinvention and not according to the invention are made and compared. Inthe compositions, a cement-based composition of 80% by weight mortarcement and 20% by weight of a metakaolin (the metakaolin is varied asspecified below) is combined with water with a water-to-cement ratio of0.4. Sand is added as aggregate in an amount so that thesand:cementitious weight ratio is 2.75 (cementitious in these examplesrefers to mortar cement and metakaolin). Comparative Example 1 is madewith metakaolin (untreated). Comparative Example 2 is made with drymilled metakaolin (ball milled for 6 hours). Comparative Example 3 ismade with metakaolin that is slurried and spray dried. Example 1 is madewith metakaolin that is wet milled (in a Netzsch mill for 5 minutes),spray dried, and pulverized. Example 2 is made with metakaolin that iswet milled (in a Netzsch mill for 5 minutes) and spray dried. Example 3is made with metakaolin that is wet milled (in a sedimentary delaminatorfor 15 minutes), oven dried, and pulverized.

[0061] The extent of dissolution of aluminum and silicon ions incompositions made with pozzolans manufactured according to the presentinvention and not according to the invention is examined. Generally, thehigher dissolution of aluminum and silicon ions, the faster thecomposition reacts. Dissolution is measured by quantifying the amount ofleaching in a 30% KOH solution. The results are reported in Table 1.TABLE 1 5 minute leach 15 minute leach Example Al, ppm Si, ppm Al, ppmSi, ppm C. Ex. 1 50 60 — — C. Ex. 2 418 318 462 379 C. Ex. 3 69 69 90 90  Ex. 1 272 245 364 348 Ex. 2 180 162 258 246 Ex. 3 136 122 170 158

[0062] The extent of potassium silicate absorption in compositions madewith pozzolans made according to the present invention and not accordingto the invention is examined next. Generally, the lower the potassiumsilicate absorption, the lower the water demand of the composition (andthus a higher resultant compressive strength). Potassium silicateabsorption is measured by quantifying the amount of potassium silicateabsorbed in a 30% KOH solution. The results are reported in Table 2.Although Comparative Example 2 has a low potassium silicate absorption,it involves dry milling metakaolin for 6 hours while Examples 1, 2, and3 involve wet milling metakaolin for 5 minutes, 5 minutes, and 15minutes, respectively, which is an enormous time savings in themanufacturing process. TABLE 2 Example potassium silicate absorption C.Ex. 1 0.9 C. Ex. 2 0.6 C. Ex. 3 0.83 Ex. 1 0.62 Ex. 2 0.63 Ex. 3 0.58

[0063] The flowability of compositions made with pozzolans madeaccording to the present invention and not according to the invention isexamined in accordance with ASTM 230. Generally, the higher the flow,the lower water demand of the composites made in accordance with thepresent invention. Flowability of the fresh mortar can also be used as ameasure of the workability of a given mixture. The results are reportedin Table 3. TABLE 3 Example Flow C. Ex. 1 47 mm Ex. 3 56 mm

[0064] The compressive strength over time is examined. Each mortarcomposition is formed into a 2 inch cube and the compressive strength istested. The reported compressive strengths represent the average oftesting two cubes (for each composition at each testing age). When notunder testing, the mortar cubes are stored in lime water. The resultsare reported in Table 4. TABLE 4 Compressive Strength (psi) Testing Age(days) Ex. 3 C. Ex. 1 1 3,665 3,810 3 6,840 6,500 7 8,845 8,385 28 9,7109,455

[0065] Two additional mortar compositions, one according to the presentinvention and one not according to the invention are made and compared.In the two compositions, a cement-based composition of 80% by weightmortar cement and 20% by weight of a metakaolin (the metakaolin isvaried as specified below) is combined with water with a water-to-cementratio of 0.4. The same amount of water is added to each of the twocompositions. Sand is added as aggregate in an amount so that thesand:cementitious weight ratio is 2.75 (cementitious in these examplesrefers to mortar cement and metakaolin). Comparative Example 4 is madewith metakaolin (untreated). Example 4 is made with metakaolin that iswet milled (in a Netzsch mill for 5 minutes) and spray dried.

[0066] The flowability of the two compositions is examined in accordancewith ASTM 230. Generally, the higher the flow, the lower water demand ofthe composites made in accordance with the present invention.Flowability can also be used as a measure of the workability of a givenmixture. The results are reported in Table 5. TABLE 5 Example Flow C.Ex. 4 40 mm Ex. 4 47 mm

[0067] The compressive strength over time is examined. Each mortarcomposition is formed into a 2 inch cube and the compressive strength istested. The reported compressive strengths represent the average oftesting two cubes (for each composition at each testing age). When notunder testing, the mortar cubes are stored in lime water. The resultsare reported in Table 6. TABLE 6 Compressive Strength (psi) Testing Age(days) Ex. 4 C. Ex. 4 1 3,930 3,840 3 6,785 6,675 7 8,425 8,335 28 9,6309,630

[0068] In one embodiment, the amount of water combined with thecement-based compositions and alkali-activated systems according to thepresent invention is about 5% less than that required to obtain the sameflowability compared to conventional cement-based compositions andconventional alkali-activated systems such as those made withconventional pozzolans including untreated metakaolin (other than water,the amounts of other components, such as optional additives, are thesame). In another embodiment, the amount of water combined with thecement-based compositions and alkali-activated systems according to thepresent invention is about 10% less than that required to obtain thesame flowability compared to conventional cement-based compositions andconventional alkali-activated systems such as those made withconventional pozzolans including untreated metakaolin (other than water,the amounts of other components, such as optional additives, are thesame). In yet another embodiment, the amount of water combined with thecement-based compositions and alkali-activated systems according to thepresent invention is about 20% less than that required to obtain thesame flowability compared to conventional cement-based compositions andconventional alkali-activated systems such as those made withconventional pozzolans including untreated metakaolin (other than water,the amounts of other components, such as optional additives, are thesame). This is a notable improvement since a lower water demand istypically associated with an increase in density and an increase instrength.

[0069] The mortar compositions made in accordance with the presentinvention not only exhibited superior workability, but also superiorcompressive strength. It is difficult to simultaneously improve bothworkability and compressive strength, yet the present invention providescement-based compositions and alkali-activated systems exhibiting bothimproved workability and compressive strength.

[0070] While the invention has been explained in relation to itspreferred embodiments, it is to be understood that various modificationsthereof will become apparent to those skilled in the art upon readingthe specification. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications as fall withinthe scope of the appended claims.

What is claimed:
 1. A method of making a highly reactive pozzolan, comprising: forming a slurry comprising metakaolin and a liquid; wet milling the slurry; and separating the metakaolin from the liquid to provide the highly reactive pozzolan.
 2. The method of making a highly reactive pozzolan according to claim 1 , wherein the liquid comprises water.
 3. The method of making a highly reactive pozzolan according to claim 1 , wherein the slurry comprises from about 10% to about 90% by weight of metakaolin and from about 10% to about 90% by weight of liquid.
 4. The method of making a highly reactive pozzolan according to claim 1 , wherein the slurry further comprises a dispersant.
 5. The method of making a highly reactive pozzolan according to claim 1 , wherein wet milling is conducted for a period of time from about 1 minute to about 60 minutes at a temperature from about −10° C. to about 150° C.
 6. The method of making a highly reactive pozzolan according to claim 1 , wherein the metakaolin is separated from the liquid by one of spray drying, flash drying, rotary drying, apron drying, oven drying, and mixing the slurry.
 7. The method of making a highly reactive pozzolan according to claim 1 further comprising pulverizing the metakaolin separated from the liquid to provide the highly reactive pozzolan.
 8. A method of making a cement-based composition comprising: providing a highly reactive pozzolan by forming a slurry comprising metakaolin and a liquid, wet milling the slurry, and separating the metakaolin from the liquid; and combining the highly reactive pozzolan with at least one cementitious material.
 9. The method of making a cement-based composition according to claim 8 , wherein the highly reactive pozzolan is made by heat treating hydrous kaolin, forming a slurry comprising the heat treated hydrous metakaolin and water, wet milling the slurry, and separating the metakaolin from the liquid by spray drying.
 10. The method of making a cement-based composition according to claim 8 , wherein the highly reactive pozzolan further comprises a dispersant.
 11. The method of making a cement-based composition according to claim 10 , wherein the dispersant comprises at least one of an ammonia-based dispersant, a phosphate-based dispersant, a sulfonate dispersant, a carboxylic acid dispersant and a polymeric dispersant.
 12. The method of making a cement-based composition according to claim 8 , wherein the cement-based composition comprises from about 50% to about 99.5% of the cementitious material and from about 0.5% to about 50% of the highly reactive pozzolan.
 13. The method of making a cement-based composition according to claim 8 , wherein the highly reactive pozzolan comprises from about 0.1% to about 20% by weight of the dispersant.
 14. The method of making a cement-based composition according to claim 8 , wherein the cementitious material comprises portland cement.
 15. The method of making a cement-based composition according to claim 8 , wherein the separated metakaolin is pulverized prior to being combined with at least one cementitious material.
 16. The method of making a cement-based composition according to claim 8 , wherein the metakaolin is separated from the liquid by one of spray drying, flash drying, and oven drying.
 17. A method of making a highly reactive pozzolan composition, comprising: forming a slurry comprising from about 20% to about 80% by weight of metakaolin and from about 20% to about 80% by weight of a liquid; and wet milling the slurry for a period of time from about 1 minute to about 60 minutes to provide the highly reactive pozzolan composition.
 18. A highly reactive pozzolan made according to the method of claim 1 .
 19. A cement-based composition made according to the method of claim 8 .
 20. A highly reactive pozzolan composition made according to the method of claim 17 .
 21. A method of making an alkali-activated composition comprising: providing a highly reactive pozzolan by forming a slurry comprising metakaolin and a liquid, wet milling the slurry for a period of time from about 2 minutes to about 30 minutes, and separating the metakaolin from the liquid; and combining the highly reactive pozzolan with at least one geopolymeric material.
 22. The method of making an alkali-activated composition according to claim 21 , wherein the wet milling is conducted using a Chaser mill, Cowles mill, a Colloid mill, a Duncan mill, a Kady mill, a Morehouse mill, a Muller mill, a Netzsch mill, a Premier mill, a Kotthoff mill and a sedimentary delaminator.
 23. The method of making an alkali-activated composition according to claim 21 , wherein the geopolymeric material is one or more of alumino-silicate oxide, sodium hydroxide, potassium hydroxide, water, sodium silicate, potassium silicate, Na₂O, K₂O, a zeolite, silica, and alumina.
 24. The method of making an alkali-activated composition according to claim 21 , wherein the alkali-activated composition comprises from about 40% to about 99.5% by weight of one or more geopolymeric materials and from about 0.5% to about 60% by weight of the highly reactive pozzolan.
 25. The method of making an alkali-activated composition according to claim 21 , wherein the metakaolin separated from the liquid after wet milling has from about 5% to about 75% reduction in pore volume compared to the metakaolin combined with water.
 26. An alkali-activated composition made according to the method of claim 21 . 